The Fc epsilon RI complex forms a high-affinity
cell-surface receptor interaction for the Fc region of antigen-specific immunoglobulin E
(IgE) molecules. Fc epsilonRI
controls the activation of mast cells and basophils, and participates in IgE-mediated
antigen presentation. Fc epsilon RI is the central to the
induction and maintenance of an allergic response and may confer physiological protection
in parasitic infections. This receptor induces multiple signaling pathways that control
the secretion of allergic mediators and induction of cytokine gene transcription,
resulting in secretion of molecules such as Interleukins:IL-4, IL-5, IL-6, IL-10, IL-13,
INF-Gamma (Interferon-Gamma), TNF-Alpha (tumour-necrosis factor-alpha), GCSF
(granulocyte-macrophage colony-stimulating factor) to name few [1].

Human mast cells and basophils express Fc epsilon RI that
consists of three subunits -alpha,beta, gamma, and formes tetramer (AlphaBetaGamma2).
However, the Fc epsilon RI on the surface of human monocytes
consist of alpha and gamma subunits and form a trimeric (AlphaGamma2) complex. The
Alpha-chain binding with IgE and the others subunits are essential for downstream
signaling [2].

After Fc epsilon RI aggregation by
antigen-induced-crosslinking the immunoglobulin E, beta-subunit-associated
LYN is activated and phosphorylates immunoreceptor
tyrosine-based activation motifs (ITAMs) in the beta and gamma subunits of Fc epsilon
RI. Phosphorylated ITAMs of the beta- and gamma- subunits
recruit additional molecules of LYN and
SYK. SYK binding to the
Fc epsilon RI complex is activated through conformational
changes after tyrosine phosphorylation by LYN.

Phosphorylation of GAB2 result its recruitment to
membrane and activation of Phosphatidylinositol 3-kinase
(PI3K), which catalyses the synthesis of
Phosphatidylinositol-3,4,5-trisphosphate (PIP3)
and thereby stimulates the AKT signaling pathway.

IP3 activates IR3 receptors
(IP3R) that results in the release of
Ca2+ from intracellular storage- endoplasmic
reticulum. In the endoplasmic-reticulum, calcium-bound
Calmodulin associates with and activates serine/threonine
phosphatase Calcineurin.
Calcineurin dephosphorylates
NFAT family of transcription factors leading to their
translocation to the nucleus [10].

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